Vehicles today use, for example, urea as a reductant in SCR (selective catalytic reduction) systems which comprise an SCR catalytic converter in which said reductant and NOx gas can react and be converted to nitrogen gas and water. Various types of reductants may be used in SCR systems. AdBlue is an example of a commonly used reductant.
Said SCR systems may also comprise a diesel oxidation catalyst (DOC) for converting NO gas coming from an engine to NO2 gas and situated upstream of said SCR catalytic converter.
One type of SCR system comprises a container which holds a reductant. The system also has a pump arranged to draw reductant from the container via a suction hose and to supply it via a pressure hose to a dosing unit situated adjacent to an exhaust system of the vehicle, e.g. adjacent to an exhaust pipe of the exhaust system. The dosing unit is arranged to inject a necessary amount of reductant into an exhaust system upstream of the SCR catalytic converter according to operating routines which are stored in a control unit of the vehicle.
There is constant need to reduce the amount of emissions from engines of motor vehicles. This applies not least to heavy motor vehicles such as trucks and buses, since legal requirements for ever smaller emissions are continually tightening.
Fault codes are currently generated in response to certain malfunctions or operational deviations of SCR systems of vehicles. These codes may however be too unspecific, potentially causing service staff great difficulties in identifying a source of malfunction in an SCR system. In certain cases where fault codes pertaining to SCR systems are generated, it may be that some other system is not operating as intended, which may in turn adversely affect the SCR system, with consequent incorrect generation of fault codes for the SCR system.
Although it may be difficult to exactly identify which component of an SCR system is faulty, it is desirable to at least be able to rule out one or more of them. This is particularly relevant in the case for example of an SCR catalytic converter, since removing this component from the vehicle, e.g. for visual examination or other investigations by troubleshooting methods, is expensive and time-consuming.
It is also particularly relevant in the case for example of a diesel oxidation catalyst, since removing this component from the vehicle, e.g. for visual inspection or investigation by other troubleshooting methods, is likewise expensive and time-consuming.
US 2011296905, DE102010028846 and US201032605 describe various methods for troubleshooting in an SCR system.